The invention relates generally to gas turbine engines and in particular to methods and apparatus for measuring, selecting, and assembling the nozzle assemblies for the nozzle in a turbine engine.
The nozzle flow area of a turbine engine and the distribution of gases around the nozzle are important parameters which affect the efficiency and operation of the turbine engine. The closer the air flow area is to the manufacturer's specifications and the more uniform the air flow is around the circumference of the nozzle, the more apt is the engine to perform reliably and efficiently. In particular, the engine is more likely to achieve a lower fuel consumption, which translates into significant fuel savings for both the engine user and the country.
During normal use, various parts of the engine must be either maintained, repaired, or replaced. In particular, in connection with the nozzle structure, one or more of the partial nozzle assemblies which form the completed nozzle will be reconditioned, replaced, or repaired, and proper maintenance of the nozzle is particularly important because the dimensional tolerances are very small. However, when a nozzle is first manufactured, or when one or more nozzle partial assemblies are removed from the nozzle structure for reconditioning, repair, or replacement, the worker who constructs or reconstructs the nozzle has the significant problem of meeting the small dimensional tolerances specified by the manufacturer with nozzle assemblies in which very small changes in vane airfoil orientation can effect relatively large changes in gas flow area. To aid him with his task, several devices have been employed.
The most reliable and accurate practical device for aiding in the construction or reconstruction of the turbine nozzle is the open area comparison gage described and claimed in Plante, U.S. Pat. No. 3,115,711, assigned to the assignee of this invention. The disclosure of U.S. Pat. No. 3,115,711 is incorporated herein by reference. This gage provides a measure of the mechanical open area between two adjacent, juxtaposed vane airfoils and the resultant readings accurately describe the effective nozzle flow area or throat area between the two vane airfoils being measured. This open area measurement correlates directly to the "class" of the vane airfoils being measured and provides the worker in the field or at the manufacturing facility with precise information useful in predicting how the turbine nozzle will function.
However, the commercial use of the open area comparison gage, which is manufactured commercially by the assignee of this invention, The L.S. Starrett Company, has been limited to those circumstances wherein the user has two or more vane airfoils in juxtaposition so that measurements may be made between them. The vane airfoils can be joined together as an integral unit (hereinafter designated a multi-vane airfoil assembly) or each vane airfoil can itself be a separate element (hereinafter designated a single vane airfoil assembly). The measurements can be made, for example, in a specially designed staging fixture for holding a multi-vane assembly, or the measurements may be made in a fixture which corresponds to a full (or partial) circumference of the turbine engine. In either case, so long as the open area measurements meet the design specifications set by the manufacturer, the end user is certain to have a resulting turbine nozzle which performs satisfactorily and reliably.
As single vane airfoil assemblies are more often adopted for use in turbine engines, there has arisen an increasing requirement to characterize in some manner a vane airfoil assembly having one vane. Generally, the requirement has been met, when open area measurement is employed, by placing two single vane assemblies in a butt-to-butt relationship and the open area between the two vanes is measured with the open area comparison gage noted above. Thereafter, one of the vanes is removed, the remaining vane is moved to the position previously occupied by the first (now removed) vane, and a new vane is inserted into the fixture in order to find a satisfactory "new vane" which meets the required specifications. While this method produces a satisfactory and reliable turbine nozzle, it is tedious and time consuming.
In addition to the present apparatus and methods for characterizing vane airfoil assemblies, there is to date no satisfactory automated method for constructing a turbine nozzle for the plurality of partial nozzle assemblies. Each partial assembly can have one or more vane airfoils. An automated process and system would not only reduce the costs of manufacturing and refurbishing the engine turbine nozzles, but would provide the end user and the original equipment manufacturer with a simplified method of forming the turbine nozzle assemblies at minimum cost and with high operating performance and reliability.
It is therefore a principal object of this invention to provide an apparatus and method for characterizing the effective throat area of a partial nozzle assembly, having one vane airfoil. A further primary object of the invention is to provide an automated method and apparatus for assembling a turbine nozzle assembly from a plurality of previously measured partial nozzle assemblies to achieve a required total area and uniform gas flows. Other objects of the invention are a method and apparatus for constructing a turbine nozzle or a portion of a turbine nozzle which is simple, highly reliable, and which preferably employs the open area comparison gage described and claimed in U.S. Pat. No. 3,115,711.